Quartz crystals are typically employed as reference frequency sources in electronic systems due to their outstanding performance characteristics. Most electronic systems include at least one high frequency (e.g., MHz) crystal. High frequency crystals provide excellent phase noise, stability, and aging characteristics but have the drawback of consuming more power than lower frequency crystals. Thus, a high frequency crystal may be employed in a system when power consumption is not constrained. However, when power conservation is critical, use of a high frequency crystal may be unacceptable. Consequently, most systems also include at least one low frequency (e.g., 32.768 kHz) crystal for low power consumption needs. The low frequency crystal compromises phase noise, some stability, and some aging characteristics in return for a substantially lower power consumption.
Existing electronic systems typically include a plurality of crystals from which to generate required system frequencies under various operating conditions. For example, a typical notebook computer may include as many as nine crystal frequency sources. Although the reference frequency generated by a single high frequency crystal can be used to generate any required system frequency, the high frequency crystal consumes too much power and thus cannot be employed when power consumption is critical. Although the reference frequency generated by a single low frequency crystal can be used to generate any required system frequency, the low frequency crystal introduces unacceptable phase noise, e.g., when coupled to a phase-locked loop, and thus in many cases cannot be employed to generate other required system frequencies. No viable techniques exist for eliminating the need for a plurality of crystal frequency sources in electronic systems.